1. Field of the Invention
The present invention relates to functional fluids. More particularly, the invention relates to certain chlorinated aromatic compounds having superior fire resistance and biodegradability, and which are especially useful as dielectric fluids or impregnants in electrical capacitors and transformers, heat transfer fluids, hydraulic fluids, plasticizers or dye solvents.
2. Description of the Prior Art
It has become increasingly important that the potential harm to the ecology be minimized in the use of materials as dielectric fluids, heat transfer fluids, hydraulic fluids and the like. For example, a modern dielectric fluid must possess a unique combination of electrical characteristics and physical properties while minimizing adverse environmental effects. Fire resistance is a very desirable property in order to avoid secondary damage should failure of the electrical device cause electrical sparks or excessive heat.
Chlorinated aromatic compounds have long been known and preferred as dielectric fluids for electrical apparatus. The most familiar fluids in this class are known as "Askarels". Askarel dielectric fluids are fire resistant, have a relatively high dielectric constant, and are by far the most widely accepted fluid for use today in electrical capacitors and transformers. Askarel fluids are formulations composed primarily of polychlorinated biphenyls which are sometimes mixed with chlorobenzenes to give particular viscosity characteristics.
Certain of the polychlorinated biphenyls, however, have been discovered to be resistant to natural degradation and, when released into the environment, these materials may enter the life cycle and be potentially harmful to ecology. Even though capacitors and transformers are customarily sealed units and escape of the dielectric fluid (or impregnant) into the environment can be prevented to a large degree, it has nevertheless become desirable to provide an alternate fluid which does not contain a major component having environmental persistence. Such an alternate fluid would also be of interest in other applications where similar environmental concerns exist.
Halogenated aromatic compounds other than polychlorinated biphenyls have been heretofore disclosed as dielectric fluids for electrical apparatus. U.S. Pat. No. 2,617,770, issued Nov. 11, 1952, broadly discloses "halogenated compounds of naphthalene, toluene, benzene, nitro-diphenyl, diphenyl oxide, diphenyl ketone, diphenyl methane, diphenyl ethane, terphenyls and quaterphenyls". Similarly, U.S. Pat. No. 2,410,714, issued Nov. 5, 1946, discloses "chlorinated benzene, chlorinated diphenyl oxide, chlorinated diphenyl methane, chlorinated diphenyl benzene and alkyl derivatives thereof".
U.S. Pat. No. 2,012,302, issued Aug. 12, 1935 to F. M. Clark et al describes various halogenated compounds said to be useful as dielectric media, heat transfer media and lubricants. A wide variety of compositions comprising halogenated compounds in which phenyl groups are linked together by carbon atoms are disclosed.
U.S. Pat. No. 2,600,691, issued June 17, 1952 to S. D. Ross et al discloses a wide variety of halogenated aromatic compounds said to be useful for electrical applications and as heat transfer agents, plasticizers for resins, and modifiers for lubricating oils.
Notwithstanding the early patent disclosures referred to above, wide commercial acceptance of halogenated aromatic compounds as dielectric fluids has been confined through the years to polychlorinated biphenyls. The other known halogenated aromatics having possible utility as dielectric fluids never achieved commercial significance for one or more technical or economic reasons. Thus, recently published efforts to provide alternate dielectric fluids for capacitors and transformers have, for the most part, been directed away from halogenated aromatic compounds because of the environmental persistence incurred with certain of the polychlorinated biphenyls.
It is an object of the present invention to provide electrical devices containing readily biodegradable dielectric fluids. It is a further object of this invention to provide improved electrical capacitors and transformers containing fire resistant, yet readily biodegradable, dielectric fluids.
Still another object of the present invention is to provide fire resistant, readily biodegradable functional fluids having outstanding viscosity properties for use as dielectric fluids, heat transfer fluids, hydraulic fluids, plasticizers or dye solvents. Other objects of this invention will become apparent from the following description and claims.